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ST/SG/AC.10/C.3/2010/33
United Nations
Secretariat
Distr.: General
31 March 2010
Original: English
Committee of Experts on the Transport of Dangerous Goods
and on the Globally Harmonized System of Classification
and Labelling of Chemicals
Sub-Committee of Experts on the Transport of Dangerous Goods
Thirty-seventh session
Geneva, 21–30 June 2010
Item 4 of the provisional agenda
Electric storage systems
Transport requirements for ultracapacitors (Electric Double
Layer Capacitors)
Transmitted by the Kilo Farad International (kFI)1
Introduction
1.
At the last session, Kilo Farad International (kFI) submitted a proposal for a new
proper shipping name for ultracapacitors with the objective of defining transport
requirements specific to these energy storage devices.
2.
to:
In particular, kFI seeks to establish transport requirements specific to ultracapacitors
• Establish measures to avoid electrical short circuiting;
• Define appropriate transport requirements;
• Identify a size range not subject to the Model Regulations; and
• Identify requirements applicable to ultracapacitors in equipment.
I. Ultracapacitor description
3.
Detailed descriptions of ultracapacitors were provided in earlier kFI documents,
particularly ST/SG/AC.10/C.3/2009/13. Briefly, ultracapacitors are energy storage devices
1
GE.
In accordance with the programme of work of the Sub-Committee for 2009-2010 approved by the
Committee at its fourth session (refer to ST/SG/AC.10/C.3/68, para. 118 (a) and ST/SG/AC.10/36,
para. 14).
ST/SG/AC.10/C.3/2010/33
that are being used increasingly in response to growing interest in energy conservation and
reduction of green-house gas emissions. One of the many applications is in automobiles
where they are used to store the electricity produced by regenerative braking systems. They
are ideal for applications where there is a need to store and release energy quickly. In other
instances, they are an alternative to batteries (e.g., in wind turbines) in view of their
reliability and long life.
4.
Ultracapacitors consist of two layers of activated carbon mixed with an electrolyte
separated by a membrane. All but a small excess (a few ml) of electrolyte is absorbed by
the activated carbon. The layers are frequently rolled up in a “jelly roll” and housed in a
cylindrical aluminium receptacle. Currently, electrolyte liquids in common use consist
either of a solution of approximately 70% acetonitrile mixed with inorganic salts or a non
dangerous organic liquid (polypropylene carbonate) combined with salts. Ultracapacitors
utilizing other electrolyte solutions are believed to be in the design stage but are not
commercially available.
II. Discussion of potential hazards
A.
Electrical hazard
5.
Considering the majority of the electrolyte is absorbed and the robust construction of
the ultracapacitor receptacle, kFI considers the electrical hazard to be the primary hazard.
The hazard is related to the potential to accidentally short circuit in transport. This hazard
is common to utracapacitors independent of the electrolyte used. For this reason kFI
recommends establishment of minimum requirements for all ultracapacitors.
6.
Unlike some other electric energy devices, there is no need to keep ultracapacitors or
ultracapacitor modules in a charged condition. kFI proposes that ultracapacitors be
required to be transported uncharged. To verify and ensure they are uncharged, we propose
that the terminals on ultracapacitors with a capacitance greater than 100 Farad, be
electrically connected by a conductive material.
7.
This is impracticable for small ultracapacitors with a capacitance of 100 Farad or
less and, for these ultracapacitors, we propose that they be protected against short circuit.
8.
kFI anticipates that it should be possible to transport most ultracapacitors in
equipment in an uncharged state. However, at least one vehicle manufacturer has indicated
that it would be impractical to ensure that ultracapacitors installed in a vehicle are
discharged when offered for transport. For ultracapacitors in equipment, we propose that
they also be transported discharged and otherwise that they be protected against short
circuiting.
B.
Flammable liquid hazard
9.
As noted, some ultracapacitors contain an electrolyte mixture of acetonitrile
(approximately 70%) and inorganic salts. The salts are non combustible and reduce the heat
content relative to pure acetonitrile. The electrolyte solution is absorbed onto activated
carbon. Manufacturers typically include a small excess amount of electrolyte (ranging up to
6 ml for the largest currently available) to ensure complete wetting of the activated carbon.
The ultracapacitor casing is robust to withstand any potential pressure build up over the life
of the ultracapacitor as discussed below. kFI proposes that ultracapacitors containing
dangerous goods be subject to a 1.2 meter drop test as packaged for transport to
demonstrate the ability to retain their contents.
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C.
Pressure hazard.
10.
There is no measurable pressure inside a new ultracapacitor. But pressure may build
up over the useful life. The amount of pressure depends on the operating temperature and
the charge voltage over the life of the ultracapacitor. There is no appreciable build up if an
ultracapacitor is maintained at 25ºC and charged at its rated voltage. The relationship
between pressure build up and charging voltage is illustrated in the following graph.
Figure shown above: Internal pressure buildup
in an ultracapacitor over time at 65°C temperature
as a function of operating voltage
11.
The relationship between pressure buildup and temperature at the rated charge
voltage (2.7 V) is illustrated in the following graph.
12.
The air space volume in an ultracapacitor represents approximately 3% of the total
volume of the ultracapacitor receptacle. For the current largest ultracapacitor design of
10 kF, the amount of free space is less than 10 ml. Even though the pressure inside the
ultracapacitor may attain 15 bar over the life of the ultracapacitor under adverse conditions,
the amount of stored energy is minimal. To address pressure concerns, an ultracapacitor is
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either fitted with a vent or a weak point is built into the ultracapacitor receptacle so that it
fails safely. To demonstrate the minimal risk posed by pressure buildup, kFI has prepared a
series of videos that will be shared with Sub-Committee participants.
13.
To address the concern for pressure buildup, kFI recommends a requirement
indicating that ultracapacitors must be designed to safely relieve pressure.
III. KFI's proposed approach in considering options for
regulating ultracapacitors
14.
It is kFI’s opinion that ultracapacitors that meet certain requirements addressing the
potential hazards described above should be permitted to be transported without having to
meet all of the requirements generally applicable to dangerous goods. Applicable
requirements should deal with the potential for short circuiting, retention of the electrolyte
within the ultracapacitor receptacle and safe control of potential pressure build up. On this
basis, kFI’s proposal is to apply these conditions to all ultracapacitors containing dangerous
goods but to except those with a capacitance of less 10 kF or less (the maximum size limit
currently produced) from other requirements of the UN Model Regulations. For
ultracapacitors with no dangerous goods, kFI would propose to except them from other
requirements if the electrical hazard and the hazard of potential pressure build up is
addressed. KFI considers the risks associated with transporting ultracapacitors to be
considerably lower than those for non spillable batteries (UN2800) which may be
transported as non dangerous with no regard to size, no requirement to demonstrate
integrity and are transported in a charged state provided the conditions in SP238 are met.
15.
Based on comments, kFI proposes to use the proper shipping name, “CAPACITOR,
electric double layer”. Hereafter in the discussion, the term capacitors refers to
ultracapacitors or electric double layer capacitors (EDLC).
IV. Evaluation of options for regulating ultracapacitors
16.
As agreed at the last meeting of the Sub-Committee, kFI has evaluated possible
options for including requirements for capacitors in the United Nations Model Regulations.
A number of possible approaches were considered based on discussions to date. These
options are described and advantages and disadvantages are considered in the following
paragraphs.
A.
Option 1
17.
Transport capacitors as Class 9 under the existing UN 3363 Dangerous Goods in
Apparatus without amendment of SP 301. SP301 permits up to the limited quantity amount
of electrolyte to be contained in apparatus. No changes to the recommendations are
required.
Advantages
• Existing entry, no need to develop a new entry.
• The 1 liter limit on the amount of liquid permitted covers the full capacitor size
range.
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Disadvantages
• The short circuit risk is not addressed.
• Under ICAO there is a 0.5 liter liquid limit per package for UN 3363. The 0.5 liter
limit accommodates existing capacitor designs when shipped as individual units.
But amendments to accommodate capacitor modules with an aggregate quantity of
liquid exceeding 0.5 liters are needed.
• All capacitors independent of size would be regulated, including capacitors installed
in equipment (e.g., automobiles, wind turbines, aircraft doors).
B.
Option 2
18.
Revise SP 301 and transport capacitors as Class 9 under UN 3363 Dangerous Goods
in Apparatus.
19.
Under this option, SP301 would be amended by adding the following paragraph:
“Electric double layer capacitors, may be transported under this entry provided:
(a)
They are transported in an uncharged state;
(b)
Each capacitor or capacitor module is fitted with a metal strap connecting the
terminals or for capacitors with a capacitance of 100 Farad or less, protected against
short circuit;
(c)
Capacitors installed in equipment are transported uncharged or protected
against short circuiting; and
(d)
Capacitors shall be designed to withstand a 95 kPa pressure differential and
shall be designed to safely relieve any pressure buildup through a vent or a weak
point in the receptacle.
Capacitors containing no dangerous goods, as indicated by a marking that
states “No DG”, and meeting the conditions in paragraphs (a) to (d) are not subject
to other provisions of these Regulations.
Capacitors with a marked capacitance of 10 kF or less are not subject to other
provisions of these Regulations when they meet the conditions in paragraphs (a) to
(d) and withstand a 1.2 meter drop test as packaged for transport.".
Advantages
• Existing entry, no need to develop a new entry, minimal changes to the Special
Provision.
• Capacitors of all sizes are accommodated.
• The short circuit risk and pressure buildup risk are addressed, irrespective of the
electrolyte used.
Disadvantages
• The presence of flammable liquid is not communicated by the assigned class in the
case of capacitors containing flammable liquid electrolyte.
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C.
Option 3
20.
Introduce a new entry in Class 9 for capacitors.
21.
The new table entry would read as follows:
(1)
XXXX
22.
(2)
(3)
CAPACITOR, electric
double layer
9
(4)
(5)
(6)
(7a)
(7b)
(8)
AAA
None
E0
P003
(9)
(10) (11)
The accompanying special provision AAA would read:
“AAA This entry applies to energy storage devices known as Electric Double Layer
Capacitors (EDLCs). EDLCs transported under this entry must meet the following
conditions:
(a)
They are transported in an uncharged state;
(b)
Each capacitor or capacitor module is fitted with a metal strap connecting the
terminals or for capacitors with a capacitance of 100 Farad or less, protected against
short circuit;
(c)
Capacitors installed in equipment are transported uncharged or protected
against short circuiting; and
(d)
Capacitors shall be designed to withstand a 95 kPa pressure differential and
shall be designed to safely relieve any pressure buildup through a vent or a weak
point in the receptacle.
Capacitors containing no dangerous goods, as indicated by a marking that
states “No DG”, and meeting the conditions in paragraphs (a) to (d) are not subject
to other provisions of these regulations.
Capacitors with a marked capacitance of 10 kF or less are not subject to other
provisions of these regulations when they meet the conditions in paragraphs (a) to
(d) and are capable of withstanding a 1.2 meter drop test as packaged for transport.".
Advantages
• The short circuit risk and pressure buildup risk are addressed, irrespective of the
electrolyte used.
• Assignment to class 9 is consistent with treatment of other equipment or apparatus
containing small amounts of dangerous goods.
• Capacitors of all sizes are accommodated.
Disadvantages
• The presence of flammable liquid is not communicated by the assigned class in the
case of capacitors containing flammable liquid electrolyte.
D.
Option 4
23.
Introduce new entries for capacitors for each class of electrolyte used and a separate
entry in Class 9 for capacitors containing non dangerous electrolyte.
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24.
Currently, entries in Class 3 and 9 would be needed. Future additional entries for
other classes (e.g., Class 8) may also be needed. New requirements for a class 3 entry
would be as follows:
(1)
XXXX
25.
(2)
(3) (4)
CAPACITOR, electric double 3
layer, containing flammable
liquid electrolyte
(5)
(6)
(7a) (7b) (8)
(9)
AAA None E0 P003
(10) (11)
The accompanying special provision AAA would read:
“AAA This entry applies to energy storage devices known as Electric Double Layer
Capacitors (EDLCs). EDLCs transported under this entry must meet the following
conditions:
(a)
They are transported in an uncharged state;
(b)
Each capacitor or capacitor module is fitted with a metal strap connecting the
terminals or for capacitors with a capacitance of 100 Farad or less, protected against
short circuit;
(c)
Capacitors installed in equipment are transported uncharged or protected
against short circuiting; and
(d)
Capacitors shall be designed to withstand a 95 kPa pressure differential and
shall be designed to safely relieve any pressure buildup through a vent or a weak
point in the receptacle.
Capacitors with a marked capacitance of 10 kF or less are not subject to other
provisions of these Regulations when they meet the conditions in paragraphs (a) to
(d) and are capable of withstanding a 1.2 meter drop test as packaged for transport.”.
26.
New requirements for a class 9 entry would be as follows:
(1)
(2)
(3) (4) (5) (6)
(7a) (7b) (8)
(9) (10) (11)
YYYY CAPACITOR, electric
9
BBB None E0 P003
double layer, containing non
dangerous electrolyte
27.
The accompanying special provision BBB would read:
“BBB This entry applies to energy storage devices known as Electric Double Layer
Capacitors (EDLCs). EDLCs transported under this entry must meet the following
conditions:
(a)
They are transported in an uncharged state;
(b)
Each capacitor or capacitor module is fitted with a metal strap connecting the
terminals or for capacitors with a capacitance of 100 Farad or less, protected against
short circuit;
(c)
Capacitors installed in equipment are transported uncharged or protected
against short circuiting; and
(d)
Capacitors shall be designed to withstand a 95 kPa pressure differential and
shall be designed to safely relieve any pressure buildup through a vent or a weak
point in the receptacle.
Capacitors containing no dangerous goods, as indicated by a marking that states “No
DG”, and meeting the conditions in paragraphs (a) to (d) are not subject to other provisions
of these regulations.
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Advantages
• Places ultracapacitors in the class that reflects the hazard of the electrolyte.
• Addresses the short circuit and pressure buildup risk regardless of electrolyte used.
Disadvantage
• Approach is not consistent with the approach taken for UN3363 which allows small
quantities of dangerous goods in machinery or apparatus to be treated as Class 9.
• Requires more entries and special provisions.
• While the provisions of the class 9 entry would apply, the entry itself would not
normally appear on transport documents.
V.
KFI evaluation of options
28.
KFI believes that option 1 does not provide an adequate level of safety and should
be rejected. The other three options provide an equivalent level of safety. While we can
agree with any of these options, options 2 and 3 appear to be most consistent with the
treatment of other machinery and apparatus where small quantities of dangerous goods are
involved. This is not the case with option 4. Considering that in the future a new entry for
asymmetric capacitors will be needed, kFI recommends option 3.
VI. KFI Proposal
29.
KFI recommends that the Sub-Committee adopt the proposal given in option 3.
30.
KFI also proposes the following consequential amendment to the table in paragraph
1.2.2.1:
Farad
8
F
-
1F = Ampere x s/V